1. Field of the Invention
The present invention relates to a wheel alignment adjusting device for adjusting alignment of wheels of a vehicle.
2. Description of the Related Art
Generally, wheels of a vehicle are provided with a camber angle for ensuring traveling stability of the vehicle, and are provided with a toe angle for preventing irregular wear caused by the provision of the camber angle.
Or, conversely, a toe angle is provided in order to balance the forces generated at the front tires and at the rear tires of the vehicle so as to ensure travelling stability of the vehicle, and the toe angle and the camber angle are combined so as to carry out adjustment for improving the traveling stability of the vehicle and minimizing the irregular wear of the tire under limiting conditions such as the structural dimensions of the vehicle and the like.
Accordingly, in order to improve the traveling stability and irregular wear resistance of the tire when the vehicle is traveling, it is important to adjust the toe angle and the camber angle, which are positional angles (wheel angles) applied to each wheel.
Adjustment of the toe angle and the camber angle is carried out with the vehicle disposed on a wheel alignment adjusting device.
In recent years, the number of highways has increased such that improvement of stability of the vehicle at a minute rudder angle has come to be desired.
On the other hand, the above-described stability of the vehicle at the minute rudder angle is largely affected by wheel alignment (positional angles applied to each wheel).
Conventionally, the toe angle of a wheel has been measured by various types of measuring devices and adjusted, for example, to an adjusted value specified by a vehicle manufacturer.
However, a device which can measure minute angles of a tire is expensive and it takes time to measure the angle. (In order to measure the angle in seconds, the position of the wheel is measured in detail by a laser (e.g., Japanese Patent Application Laid-Open (JP-A) No. 9-280843, JP-A-9-329433), or by a potentiometer (JP-A-7-35652), or by a dial gauge, and the minute angle is calculated.)
On the other hand, even if the adjustment of wheel alignment is carried out based on a value which is set by the manufacturer, manufacturing errors when the vehicle is manufactured, deterioration of a bush or a damper due to changes with time, twisting of the vehicle body, setback (difference between left and right wheel bases) of the wheels, and further, errors in the characteristics of the tire, or the like can occur. Consequently, the value set by the manufacturer is not always the best set value for the current vehicle.
As a result, for example, JP-A-7-5076 discloses a method of adjusting alignment which takes the above-described manufacturing errors of the vehicle body and the like into consideration and which does not use the value set by the manufacturer.
In the method disclosed in JP-A-7-5076, for example, in order to adjust the toe angle of a rear wheel, the rear wheel is loaded on a roller of a loading stand and rotated. Then, the positional angle of the rear wheel is adjusted so that the force generated at the roller in a rotational axial direction is minimized.
However, the positional angle of the wheel needs to be changed various times in order to collect data and find the best point. Also, adjustment of the toe angle must be carried out a plurality of times. Thus, complexity of the operation is not solved.
With the aforementioned in view, an object of the present invention is to provide a wheel alignment adjusting device in which alignment can be carried out easily and in a short time, and, in particular, adjustment of a toe angle can be effected accurately and precisely.
A first aspect of the present invention is a wheel alignment adjusting device, comprising: a unit which includes a wheel rotating device which rotates wheel of a vehicle loaded on the wheel alignment adjusting device; a base which rotatably supports said unit on a horizontal surface; a rotational angle detecting device which is mounted to one of said unit and said base and which detects a rotational angle by rotating a rotational shaft of said rotational angle detecting device; and an elongated member, one portion of the elongated member being trained around the rotational shaft and another portion of the elongated member being anchored to a predetermined position of another of said unit and said base, the predetermined position being separated, in a radial direction, from a rotational center of said unit by a distance which is greater than a radius of the rotational shaft.
For example, the rotational angle detecting device is mounted to the unit. The one portion of the elongated member (e.g., a wire) is trained around the rotational shaft of the rotational angle detecting means, and the other portion of the elongated member is anchored to the base. When the unit is rotated with respect to the base, the elongated member rotates the rotational shaft of the rotational angle detecting means.
Because the elongated member is anchored to a position which is separated, in the radial direction, from the rotational center of the unit by a length which is larger than the radius of the rotational shaft of the rotational angle detecting device, the rotational angle of the rotational shaft is larger than the rotational angle of the unit (rate of magnification of the angle =distance from the rotational center of the unit to the anchored position of the wire/radius of the rotational shaft of the rotational angle detecting device).
As a result, the rotational angle of the unit can be measured more precisely and accurately than a case in which the ratio of the rotational angle of the unit to the rotational angle of the rotational shaft of the rotational angle detecting device is 1 to 1 (direct transmission).
Needless to say, the larger the rate of magnification, the more minute the rotational angle of the unit which can be measured.
Further, the wheel loaded on the unit can be rotated by the wheel rotating means. At this time, force which is applied from the wheel to the wheel rotating device can be measured by a force sensor which is further included in the wheel alignment adjusting device of the first aspect.
Next, description will be given of a method of adjusting wheel alignment by using the wheel alignment adjusting device. As an example, a method of adjusting toe angles of the rear wheels will be described.
Each of the rear wheels is loaded on the unit and rotated by the wheel rotating device. At this time, force of one rotation of the wheel which is applied to the unit in the rotational axial direction of the wheel is measured by the force sensors, and the measured data is collected. The collection of data is carried out separately for the left and right wheels.
Further, in the above-described collection of data, a position at which all of the rotating directions of the wheel rotating means are parallel (to the longitudinal direction of the vehicle) is a reference position. Moreover, each unit is rotated from the reference position by one predetermined angle at a time and then the measured data is collected in the same way.
Then, when the data in which the fluctuation in the force applied to the unit (applied to the roller) in the rotational axial direction of the wheel is the smallest is obtained, calculation is made as to by how many degrees the position of the unit at which the data has been obtained has deviated from the reference position. The toe angle of each rear wheel is adjusted by the calculated degrees of angle. In this way, stable traveling of the vehicle is possible.
The data of the right rear wheel and the data of the left rear wheel are compared, and thereafter, the left and right toe angles may be respectively adjusted so that the force in the rotational axial direction which is generated by the left rear wheel and the force in the rotational axial direction which is generated by the right rear wheel are offset. In this way as well, stable traveling of the vehicle is possible.
A second aspect of the present invention is a wheel alignment adjusting device according to the first aspect, further comprising: a display device which is connected to said rotational angle detecting device and which displays the rotational angle of said unit with respect to said base.
In the wheel alignment adjusting device of the second aspect, the rotating angle of the unit when rotated is displayed on the display device.
As a result, when the unit is rotated, an operator can determine accurately over what angle the unit has rotated.
A third aspect of the present invention is a wheel alignment adjusting device according to the second aspect, further comprising: a reference position detecting device which detects a reference position of said unit in a rotating direction with respect to said base, wherein said display device displays a rotational angle of said unit on the basis of the reference position.
In the wheel alignment adjusting device of the third aspect, when the unit is rotated, the rotating angle of the unit based on the reference position is displayed on the display device.
As a result, the operator can determine accurately the angle over which the unit has rotated from the reference position.
A fourth aspect of the present invention is a wheel alignment adjusting device which includes a plurality of wheel driving devices which drive wheels of a vehicle loaded on said wheel alignment adjusting device, said wheel driving device comprising: a unit which includes wheel rotating device which rotates a wheel; a base which rotatably supports said unit in a horizontal plane; a rotational angle detecting device which is mounted to one of said unit and said base, said rotational angle detecting device including a rotating member which rotates on the basis of a rotation of said unit with respect to said base, and on the basis of the rotation of said rotating member, said rotational angle detecting device detects a rotational angle of said unit with respect to said base; and a rotation transmitting member, one portion of said rotation transmitting member being mounted to said rotating member so as to have a predetermined rotating radius, and another portion of said rotation transmitting member being anchored to a predetermined position of another of said unit and said base, and said rotation transmitting member transmitting the rotation of said unit with respect to said base to said rotating member, wherein a distance between the predetermined position and a rotational center of said unit with respect to said base is larger than the predetermined rotating radius of said rotating member.
In a fifth aspect of the present invention, in the wheel alignment adjusting device of the fourth aspect, on the basis of the distance and the predetermined rotating radius, a magnification ratio, which is a ratio of the rotational angle of said rotating member with respect to the rotational angle of said unit with respect to said base, is determined.